This invention relates to an insulated nozzle for use in an interrupter.
In a puffer type of interrupter, an insulated nozzle is disposed in the vicinity of a position between a movable electrode and a fixed electrode at which an arc occurs when the interrupter interrupts a current. The insulated nozzle is adapted to blow SF.sub.6 gas into the arc, thereby reducing the period of time required to extinguish the arc.
With this type of interrupter, when the current is interrupted, an arc in the form of a high-temperature plasma occurs between the movable electrode and the fixed electrode. Conventionally, to extinguish this arc, a flow of gas, such as air or SF.sub.6 gas, is blown from a nozzle made of a fluoroplastic having insulating properties. However, there arises a problem in that when an insulator covering the nozzle surface is exposed to the arc in the form of a high-temperature plasma, the insulating property of the insulator is greatly reduced by energy lines which are generated by the arc and which not only reach the surface of the insulator but also enter thereinside so as to produce voids or deposited carbon on the surface or interior of the nozzle.
With a view to eliminating this problem, there has been disclosed an interrupter having a fluoroplastic insulator into which an inorganic filler in the form of a powder having a particle size of 3 to 20 .mu.m is mixed to a volumetric percentage of 10 to 80. For example, such a filler is formed of metal such as bronze or a metal oxide such as silicon oxide, titanium oxide or aluminum oxide. The thus produced resin insulator used in this interrupter is improved in the internal arc-resistant characteristics, which are realized by mixing a large proportion of an inorganic filler into the resin so as to provide shield against the arc's energy lines. Therefore, this insulator is effective for improving the withstand-voltage performance after repeated current interruptions. Various materials have been used as inorganic fillers to be mixed into fluoroplastic. It has been proved that boron nitride is, from the viewpoint of insulating properties and heat conductivity, one of the most suitable fillers to be mixed into the material of an insulated nozzle for use in an interrupter of ultra-high voltage ratings. For example, Japanese Patent Laid-Open No. 58-178931 discloses the fact that, if a volumetric ratio of 1 to 30 percent of boron nitride is mixed into the resin insulator, the withstand-voltage performance after repeated current interruptions is improved.
The above-described type of insulated nozzle for use in an interrupter is formed from a fluoroplastic having an inorganic filler mixed therein at a comparatively high mixing ratio in order to improve the withstand-voltage performance after repeated current interruptions. However, as is well known, if the proportion of the added inorganic filler increases, the rate at which the insulated nozzle is consumed increases, resulting in deterioration in the current interruption performance. Therefore, if the proportion of the added inorganic filler is increased in order to improve the withstand-voltage performance, the interruption performance after repeated current interruptions is reduced, and it is thus difficult to improve both the withstand-voltage performance and the interruption performance while keeping them in balance.